Add a comment about handled routes to /rest/:action
Add /rest/removebook and start tracking downloads

- Adds /rest/removebook
- Tracks dlownloads in the downloads and old_downloads tables
- Updates all Schema/Result's with a new version of DBIx::Class::Schema::Loader
- Adds some more tests in t/rest.t

TODO:
- Handle (old_)downloads in bin/returns.pl